The present disclosure relates to turbine engines, and more particularly, to a variable stator vane.
A turbine engine typically includes multiple compressor stages. Each stage includes circumferentially arranged stators positioned axially adjacent to an array of compressor blades. Some compressor stages include variable stator vanes in which the stators include trunnions that support axial rotation. The compressor section static structure may be utilized to support the outboard variable vane trunnions while a segmented split ring may be utilized to support the inboard variable vane trunnions.
In one type of variable stator vane, a leading edge of the airfoil is inset relative to the circumferences of the platforms while a trailing edge of the airfoil extends beyond, or overhangs, the platforms. The transition areas between the airfoil and the platforms may be designed to, for example, minimize stress.
One approach to minimize stress is to provide a transition fillet between the airfoil and the platforms. The fillet extends between the airfoil and each platform from the point where the airfoil trailing edge overhangs the circumference and wraps around the leading edge to the opposite side of the airfoil, terminating where the airfoil overhangs the circumference on the adjacent side. Such stator vanes may still be subject to stress in this transition area despite the use of fillets.
Another approach, which is sometimes used in combination with the above approach, is to apply a relief cut or slab-cut in the platform to interface with the trailing edge. An additional transition fillet is then applied to the slab-cut and the interfacing airfoil trailing edge. The slab-cut fillet adjoins the airfoil fillet to produce a continuous blend between the airfoil and the respective platforms.
Structural optimization balances slab-cut material removal against fillet size and trailing edge overhang. Excessive trailing edge overhang may be required for aerodynamic efficiency, but such overhang may not be conducive to structural optimization and may result in a variable vane susceptible to stress risers. These three-dimensional blends may also often only be producible by hand which may result in variation and significant manufacturing cost.
Negative aerodynamic performance effects of these fillets may include blockage in the flowpath; cavities in the flowpath caused by the flat surfaces at the leading and/or trailing edge airfoil to the platform overhang transitions; and radial gaps between the overhung airfoil and the static structure.